It is known to use water swellable polymers in water sealing applications. Generally such polymers are acrylics. That is they are based on or have a significant proportion (e.g. greater than about 60%) of a monomer such as acrylic acid or methacrylic acid. The use of these polymers is analogous to the use of swellable rubber around the wing tanks of fighter aircraft in the second world war. That is the polymer was placed on the "dry" side of a barrier. If the barrier becomes broken or ruptured, the polymer rapidly takes up the water and seals the rupture or break in the barrier. These types of barriers are important in many applications from the mundane such as barriers around substructures which extend below the water table such as the foundations and basements of buildings and/or tunnels etc. to the more exotic such as sealing means to prevent the intrusion of water into fibre optics cables.
The polymers of the present invention are not acrylic polymers. Rather, the polymers are sulphonated (vinyl) aromatic polymers.
European Patent 0 335 410 published Apr. 10, 1989 in the name of Takizawa et al, assigned to Dainichiseika Color & Chemicals Mfg. Co., Ltd. discloses the use of a water swellable polymer of hydrophobic chains having an .alpha.,.beta.-ethylenic unsaturation at the end of the chain and a monomer of (meth) acrylic acid. As noted above, the polymers of the present invention do not contain significant, if any, (meth acrylic acid. Additionally, the polymers of the present invention have a backbone which is initially hydrophobic but which is sulphonated and becomes hydrophylic. Thus, the polymers of the present invention are distinct over the polymers taught in EP 0 335 410.
The present invention seeks to provide a novel absorbent water block material comprising the class of sulphonated vinyl aromatic polymers and their use in water blocking applications. The polymers should have a swell rate so that the polymers double their volume in water or dilute salt solutions, such as sea water, in less than about 30 seconds when contacted with an equal or excess weight of water or 3% NaCl.